The present invention relates generally to the production of radioisotopes, and, more specifically, to a target for irradiation of a sample by an accelerated particle beam to produce the radioisotope.
A radioisotope may be produced by irradiating a material sample with a particle beam produced in an accelerator based on various nuclear reactions. A typical medical application is Positron Emission Tomography (PET). The nuclear medicine PET procedure is used for imaging and measuring physiologic processes within the human body. A radiopharmaceutical is labeled with a radioactive isotope and is suitably administered to a patient. The radioisotope decays inside the patient through the emission of positrons. The positrons are annihilated upon encountering electrons which produce oppositely directed gamma rays. A PET scanner includes detectors surrounding the patient which detect the paths of the gamma rays. This data is suitably analyzed to map the present of the radioisotopes in the patient for diagnostic purposes.
A typical radioisotope is Fluorine-18 (.sup.18 F) which has a very short half-life. Accordingly, the radioisotope must be produced immediately before being administered to the patient which presents a substantial problem since complex and expensive equipment is required to produce the radioisotope. Expensive particle beam accelerators are used to emit a particle beam to react with a material sample for producing the radioisotope. A high energy 12 MeV proton beam is typically produced in a cyclotron and steered to the target sample for producing a nuclear reaction to generate the desired radioisotope. The high energy proton beam requires a high power accelerator for its production although the resulting proton beam has relatively low beam current of about 10-20 microamps.
The desired sample material, in liquid, gas, or solid form, is placed in a suitably configured target for undergoing irradiation. The target may include an entrance window foil of aluminum which covers the sample and allows the high energy, low current proton beam to pass into the sample without substantial energy loss. The particle beam hits the sample in the target which must be cooled for maintaining integrity of the target and the foil window.
In order to reduce the cost of producing radioisotopes, the use of low power accelerators producing low energy particle beams is being explored. For example, a low energy 8 MeV proton beam is less expensive to produce. However, a relatively large beam current of about 100-150 microamps is required therewith for obtaining a suitably high power density in the target for producing the radioisotope. Low energy proton beams are quickly degraded by typical entrance window foils, and substantial heat energy must still be dissipated from the target.
Accordingly, it is desired to provide an improved target specifically configured for use with low energy, high current particle beams for effectively producing radioisotopes.